[Peterfrans]

The cold start enrichtment nozzles in your stacks are actuated by a solenoid on top of your fuel filter. This in turn is controlled by a thermo-time switch that sits in the breather cover on your engine case. It has no relation to the (missing) heat exchanger hose. It is just to help the engine start, after that, during the warm up phase the hot air from the heat exchanger comes into play. This controls the mixture during warm up.

So to answer your question: there is no need to block them